Have you beaten Volcano Manor yet? I would do that before Radahn and get the Blasphemous Blade from the boss remembrance at Volcano Manor. Probably the best greatsword pre DLC, especially for 'beginners'. Has a very powerful L2 attack and heals you on every kill.
I havent even gotten to Volcano Manor or Altus Plateau yet. Caria Manor + Ranni's Rise is as far North as I've gone.
On my recent playthrough, I did Volcano Manor before the Radahn festival. That said, have you fought Radahn yet? If you're already near him, I would at least try him a few times. If he's giving you too much trouble, take a break and go to Volcano Manor and clear that, then go back and try again.
It's an awesome fight, but on my OG playthrough a couple years ago, it was probably the hardest fight for me other than Malenia at the very end of the game.
Get a Brass Shield for certain fights (lots of mobs drop them) and practice guard counter (its easy and good for certain fights). Grafted will carry you a long while until you can get the Ruins Greatsword or any of the multiple weapons that drop around the same time (The "Guts" greatsword that is in a chest in the early part of Caelid is also a very popular choice you can nab early on). The Bloodhound Knight sword is also really good (you can beat the entire main game handily with it) but its a little more finesse than most Unga Bunga style weapons. The simple fact is that aside from weapon arts you only care about attack power and occasionally damage type (certain times Slash and Strike are more ideal than their opposite number). That and Guard Counters, Jump Attacks, and strong attacks all break poise rapidly with the bigger weapons. If you like dodging and are good at it, two handing is the way to go, just expect to have to drop more into vitality and endurance (to wear better armor) to offset the lack of a block.
If he has not been doing the Ranni quest line, then Radahn festival might not be triggering. He can do the rape fight in the festival area for Ruins Greatsword, in that case. BB is indead among the best weapons in the game for the art, for a two handed user with the right stats (even post nerf). But I think a properly configured "Guts" Great Sword, Ruins GS, and the boat anchor are way better for full on Unga Bunga play. Boat Anchor is really easy to get early, too.
Radahn is rough as an unga bunga. You definitely want a weapon art to be able to apply damage at range (rot dragon breath is also a big help with minimal requirements) to tackle him. Killing him as a dagger user was really aggravating, prompting me to eventually resort to spamming the Reduvia weapon art to drop him. But he can be stance broken, at least. His rewards are shit, but the bow can be fun on an Unga build with decent dex.
The "terrible" version was nerfed not long after release. Unless for some reason that was reversed later, as long as you aren't severely under-geared/under-leveled the fight's not too bad.
